{smcl}
{* *! version 0.5.0 26Jan2020}{...}
{viewerdialog greshape "dialog greshape"}{...}
{vieweralsosee "[R] greshape" "mansection R greshape"}{...}
{viewerjumpto "Syntax" "greshape##syntax"}{...}
{viewerjumpto "Description" "greshape##description"}{...}
{title:Title}

{p2colset 5 17 23 2}{...}
{p2col :{cmd:greshape} {hline 2}} Fast alternative to reshape using C for speed. {p_end}
{p2colreset}{...}

{pstd}
{it:Important}: Please run {stata gtools, upgrade} to update {cmd:gtools} to
the latest stable version.

{marker syntax}{...}
{title:Syntax}

{pstd}
{opt greshape} is a fast alternative to {opt reshape} that additionally
implements the equivalents to R's {cmd:spread} and {cmd:gather} from
{cmd:tidyr}. Further, it allows an arbitrary number of grouping by variables
({opt i()}) and keys ({opt j()}).

{p 4 8 2}
Normal syntax

{p 8 8 2} In R parlance, {opt j()} is called {opt keys()}, which is
frankly much clearer to understand. Hence, while regular Stata syntax is
also supported, {cmd:greshape} provides the aliases {opt by()} and {opt keys()}
for {opt i()} and {opt j()} respectively (note {it:spread} and {it:wide}
accept multiple {it:j} keys).

{p 8 8 2}
wide->long

{p 12 16 2}
{cmd:greshape} {helpb greshape##overview:gather}
{varlist}{cmd:,}
{cmd:keys(}{varlist}{cmd:)}
{cmd:values(}{varname}{cmd:)}
[{it:{help greshape##options_table:options}}]

{p 12 16 2}
{cmd:greshape} {helpb greshape##overview:long}
{it:stubnames}{cmd:,}
{cmd:by(}{varlist}{cmd:)}
[{it:{help greshape##options_table:options}}]

{p 8 8 2}
long->wide

{p 12 16 2}
{cmd:greshape} {helpb greshape##overview:spread}
{varlist}{cmd:,}
{cmd:keys(}{varname}{cmd:)}
[{it:{help greshape##options_table:options}}]

{p 12 16 2}
{cmd:greshape} {helpb greshape##overview:wide}
{it:stubnames}{cmd:,}
{cmd:by(}{varlist}{cmd:)}
{cmd:keys(}{varname}{cmd:)}
[{it:{help greshape##options_table:options}}]

{p 8 8 2} {it:i} and {it:j} not only look similar, but even if you are
familiar with conventional matrix notation it's not immediately obvious
which is the grouping variable and which defines the column keys. In any
case, note that in {it:spread} and {it:gather} the {opt by()} option is
implicitly defined as every variable remaining in the data.

{p 4 8 2}
Stata syntax

{p 8 8 2}
I think the above syntax is clearer (happy to receive feedback otherwise)
but {cmd:greshape} also accepts the traditional Stata {it:i, j} syntax:

{p 12 16 2}
{cmd:greshape} {helpb greshape##overview:long}
{it:stubnames}{cmd:,}
{cmd:i(}{varlist}{cmd:)}
[{it:{help greshape##options_table:options}}]

{p 12 16 2}
{cmd:greshape} {helpb greshape##overview:wide}
{it:stubnames}{cmd:,}
{cmd:i(}{varlist}{cmd:)}
{cmd:j(}{varname}{cmd:)}
[{it:{help greshape##options_table:options}}]

{p 4 8 2}
Details

{p 8 8 2}
The {it:stubnames} are a list of variable {it:prefixes}. The suffixes are either
saved or taken from {opt keys()}, depending on the shape of the data.  Remember
this picture:

               {it:long}
            {c TLC}{hline 12}{c TRC}                   {it:wide}
            {c |} {it:i  j}  {it:stub} {c |}                  {c TLC}{hline 16}{c TRC}
            {c |}{hline 12}{c |}                  {c |} {it:i}  {it:stub}{bf:1} {it:stub}{bf:2} {c |}
            {c |} 1  {bf:1}   4.1 {c |}     greshape     {c |}{hline 16}{c |}
            {c |} 1  {bf:2}   4.5 {c |}   <{hline 10}>   {c |} 1    4.1   4.5 {c |}
            {c |} 2  {bf:1}   3.3 {c |}                  {c |} 2    3.3   3.0 {c |}
            {c |} 2  {bf:2}   3.0 {c |}                  {c BLC}{hline 16}{c BRC}
            {c BLC}{hline 12}{c BRC}

            long->wide

         {col 54}{it:j} existing variable(s)
         {col 53}/
                    {cmd:greshape wide} {it:stub}{cmd:, by(}{it:i}{cmd:) keys(}{it:j}{cmd:)}

            wide->long

                    {cmd:greshape long} {it:stub}{cmd:, by(}{it:i}{cmd:) keys(}{it:j}{cmd:)}
         {col 52}\
         {col 53}{it:j} new variable

{p 8 8 2}
Additionally, the user can reshape in the style of R's {cmd:tidyr} package.
To go from long to wide:

     	    {cmd:greshape spread} {it:varlist}{cmd:, keys(}{it:j}{cmd:)}

{p 8 8 2}
Note that {cmd:spread} (and {cmd:gather}) both require variable {it:names}, not prefixes.
Further, all variables not specified in the reshape are assumed to be
part of {cmd:by()} and the new variables are simply named after the values of
{cmd:keys()}. From wide to long:

     	    {cmd:greshape gather} {it:varlist}{cmd:, keys(}{it:j}{cmd:) values(}{it:values}{cmd:)}

{p 8 8 2}
This does {opt not} check for duplicates or sorts the data. Variables not
named are assumed to be part of {cmd:by()}).  The values of the variables in
{it:varlist} are saved in {cmd:values()}, with their names saved in {it:keys()}.

{p 8 8 2}
{cmd:reshape}'s extended syntax is not supported; that is, {cmd:greshape} does
not implement "reshape mode" where a user can type {cmd:reshape long} or
{cmd:reshape wide} after the first reshape. This syntax is cumbersome to
support and prone to errors given the degree to which {cmd:greshape} had
to rewrite the base code. This also means the "advanced" commands
are not supported, including: clear, error, query, i, j, xij, and xi.

{synoptset 19 tabbed}{...}
{marker table_options}{...}
{synopthdr}
{synoptline}
{syntab :Long}
{synopt :* {opth by(varlist)}} use {it:varlist} as the ID variables (alias {opt i()}).
{p_end}
{synopt :{opth keys(varname)}} wide->long: {it:varname}, new variable to store stub suffixes (default {it:_j}; alias {opt j()}).
{p_end}
{synopt :{opt s:tring}} Whether to allow for string matches to each {it:stub}
{p_end}
{synopt :{opt match(str)}} Where to match levels of {opt keys()} in stub (default {opt @}). Use {opt match(regex)} for complex matches.
{p_end}
{synopt :{opt dropm:iss}} Drop missing observations for reshaped variables.
{p_end}

{syntab :Wide}
{synopt :* {opth by(varlist)}} use {it:varlist} as the ID variables (alias {opt i()}).
{p_end}
{synopt :* {opth keys(varlist)}} long->wide: {it:varlist}, existing variable with stub suffixes (alias {opt j()}).
{p_end}
{synopt :{opth cols:epparate(str)}} Column separator when multiple variables are passed to {opt keys()}.
{p_end}
{synopt :{opt match(str)}} Where to replace levels of {opt keys()} in stub (default {opt @}).
{p_end}
{synopt :{opt labelf:ormat(str)}} Custom label format using placeholders (only with single variable input for {opt key()}/{opt j()}). Default {it:#keyvalue# #stublabel#}. Other placeholders are {it:#stubname#}, {it:#keyname#}, {it:#keylabel#}, {it:#keyvaluelabel#}.
{p_end}
{synopt :{opt prefix(str)}} Custom renaming of reshaped variables (one rename per stub; {opt @} syntax allowed).
{p_end}


{syntab :Common long and wide options}
{synopt :{opt fast}} Do not wrap the reshape in preserve/restore pairs.
{p_end}
{synopt :{opt unsorted}} Leave the data unsorted (faster). Original sort order is {opt not} preserved.
{p_end}
{synopt :{opt nodupcheck}} wide->long, allow duplicate {opt by()} values (faster).
{p_end}
{synopt :{opt nomisscheck}} long->wide, allow missing values and/or leading blanks in {opt keys()} (faster).
{p_end}
{synopt :{opt nochecks}} This is equivalent to all 4 of the above options (fastest).
{p_end}
{synopt :{opt xi(drop)}} Drop variables not in the reshape, {opt by()}, or {opt keys()}.
{p_end}

{synoptline}
{syntab :Gather}
{synopt :* {opth values(varname)}} Store values in {it:varname}.
{p_end}
{synopt :{opth keys(varname)}} wide->long: {it:varname}, new variable to store variable names (default {it:_key}).
{p_end}
{synopt :{opt usel:abels[{cmd:(}{it:str}{cmd:)}]}} Store variable labels instead of their names (optionally specify which variables to do this for).
{p_end}
{synopt :{opt dropm:iss}} Drop missing observations for reshaped variables.
{p_end}

{syntab :Spread}
{synopt :* {opth keys(varlist)}} long->wide: {it:varlist}, existing variable with variable names.
{p_end}
{synopt :{opt labelf:ormat(str)}} Custom label format using placeholders (only with single variable input for {opt key()}/{opt j()}). Default {it:#keyvalue# #stublabel#}. Other placeholders are {it:#stubname#}, {it:#keyname#}, {it:#keylabel#}, {it:#keyvaluelabel#}.
{p_end}
{synopt :{opt prefix(str)}} Custom renaming of reshaped variables (one common rename; {opt @} syntax allowed).
{p_end}

{syntab :Common gather and spread options}
{synopt :{opth by(varlist)}} check {it:varlist} are the ID variables. Throws an error otherwise.
{p_end}
{synopt :{opt xi(drop)}} Drop variables not in the reshape or in {opt by()}.
{p_end}
{synopt :{opt fast}} Do not wrap the reshape in preserve/restore pairs.
{p_end}

{synoptline}
{syntab:Gtools Options}
{synopt :{opt compress}}Try to compress strL to str#.
{p_end}
{synopt :{opt forcestrl}}Skip binary variable check and force gtools to read strL variables.
{p_end}
{synopt :{opt v:erbose}}Print info during function execution.
{p_end}
{synopt :{opt bench}{it:[(int)]}}Benchmark various steps of the plugin. Optionally specify depth level.
{p_end}
{synopt :{opth hash:method(str)}}Hash method (default, biject, or spooky). Intended for debugging.
{p_end}
{synopt :{opth oncollision(str)}}Collision handling (fallback or error). Intended for debugging.
{p_end}

{synoptline}
{syntab:* options are required for that subcommand.}
{p2colreset}{...}

{marker description}{...}
{title:Description}

{pstd}
{cmd:greshape} converts data from wide to long form and vice versa.  It
is a fast alternative to {cmd:reshape}, and it additionally implements
{cmd:greshape spread} and {cmd:greshape gather}, both of which are
marginally faster and in the style of the equivalent R commands from
{cmd:tidyr}.

{pstd}
It is well-known that {cmd:reshape} is a slow command, and there are
several alternatives that I have encountered to speed up reshape,
including: {opt fastreshape}, {opt parallel}, {opt sreshape}, and various
custom solutions (e.g. {browse "http://www.nber.org/stata/efficient/reshape.html":here}).
While these alternatives are slower than `greshape`, the speed gains are
not uniform.

{pstd}
If {opt j()} is numeric, the data is already sorted by {opt i()}, and
there are not too may variables to reshape, then {cmd:fastreshape} comes
closest to achieving comparable speeds to {cmd:greshape}. Under most
circumstances, however, {cmd:greshape} is typically 20-60% faster than
{cmd:fastreshape} on sorted data, and up to 90% faster if {opt j()} has
string values {it:or} if the data is unsorted (by default, {cmd:greshape} will
output the data in the correct sort order). In other words, {cmd:greshape}'s
speed gains are very robust, while other solutions' are not.

{marker example}{...}
{title:Examples}

{pstd}
See the
{browse "http://gtools.readthedocs.io/en/latest/usage/greshape/index.html#examples":online documentation}
for examples.

{marker author}{...}
{title:Author}

{pstd}Mauricio Caceres{p_end}
{pstd}{browse "mailto:mauricio.caceres.bravo@gmail.com":mauricio.caceres.bravo@gmail.com }{p_end}
{pstd}{browse "https://mcaceresb.github.io":mcaceresb.github.io}{p_end}

{title:Website}

{pstd}{cmd:greshape} is maintained as part of the {manhelp gtools R:gtools} project at {browse "https://github.com/mcaceresb/stata-gtools":github.com/mcaceresb/stata-gtools}{p_end}

{marker acknowledgment}{...}
{title:Acknowledgment}

{pstd}
This help file was based on StataCorp's own help file for {it:reshape}.
{p_end}

{pstd}
{opt gtools} was largely inspired by Sergio Correia's {it:ftools}:
{browse "https://github.com/sergiocorreia/ftools"}.
{p_end}

{pstd}
The OSX version of gtools was implemented with invaluable help from @fbelotti;
see {browse "https://github.com/mcaceresb/stata-gtools/issues/11"}.
{p_end}

{title:Also see}

{p 4 13 2}
help for
{help gtools}; {help reshape}
